. Annual report. 1st-12th, 1867-1878. Geology. 6HUVELDT] OSTEOLOGY OF THE TETRAONID^E. 697 oblique ligament that is attached higher up on the inner aspect of the shaft, that also holds some of the extensor tendons in position. The condyles in mature birds have an antero-posterior position at the extremity of the tibia; these are of a uniform outline, and the inter-con- dyloid notch that separates them is of no particular depth until it arrives on the anterior aspect of the bone. Externally and laterally almost within the limits of the outline of the outer condyle we find two tuber- cles, one a
. Annual report. 1st-12th, 1867-1878. Geology. 6HUVELDT] OSTEOLOGY OF THE TETRAONID^E. 697 oblique ligament that is attached higher up on the inner aspect of the shaft, that also holds some of the extensor tendons in position. The condyles in mature birds have an antero-posterior position at the extremity of the tibia; these are of a uniform outline, and the inter-con- dyloid notch that separates them is of no particular depth until it arrives on the anterior aspect of the bone. Externally and laterally almost within the limits of the outline of the outer condyle we find two tuber- cles, one above another; the lower is for ligamentous attachment, the upper is the remnant and only existing evidence of the lower extremity of the fibula. A similar tubercle is found on the opposite, side corre- sponding to the lower one just described on the outer aspect. The fibula is freely de- tached and never completely anchyloses with the tibia. Its proximal extremity is clubbed, enlarging very much as it rises above the condylar surface of its com- panion from the fibul ar ridge; it is laterally compressed and; convex above at the summit. In many Grouse the attenu- ated remains of its extension below can be traced on the shaft of the tibia, which bone has nearly absorbed this third of its weaker associate. caiupepia squamata. In the early life of the chick of the Grouse we have been discussing, the combined tarsals are surmounted by a third plate of cartilage, that subsequently ossifies, apparently by one center. The bone thus formed, the centrale, we believe undoubtedly to represent either a single tarsal element or the connate bones of the second row. At this age the metatarsals that combine to form the shaft of the tarso-metatarsus are still easily individualized, though well on the road toward permanent fusion. It will be observed that we still retain the term tarso-metatarsus. and we think justly so, as the compound bone of the mature bird has combined with it at least one of
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